Human peripheral blood lymphocyte severe combined immunodeficiency (hu‐PBL SCID) models of toxoplasmosis

Abstract

Summary Toxoplasmosis is a potentially fatal opportunistic infection of immunocompromised hosts. Improved animal models of toxoplasmosis are needed to more nearly approximate conditions that occur in immunocompromised humans. The development of models of toxoplasmosis using human peripheral blood lymphocytes (hu-PBL) transplanted into severe combined immunodeficiency (SCID) mice is described here. Transplantation of hu-PBL into SCID mice without prior conditioning of the mice resulted in detectable differences in quantitative histological scores of brain inflammation due to Toxoplasma gondii infection, but did not alter mortality when compared to SCID mouse controls. The lack of detectable differences in survival were due to inadequate engraftment of hu-PBL, as assessed by flow cytometry. Unconditioned hu-PBL SCID mice had low titre T. gondiispecific antibody detectable after infection. When pretransplantation conditioning with irradiation and antiasialo GM 1 (n-glucolyl neuraminic acid) antibody was used, prolonged hu-PBL engraftment was observed in SCID mice, which was associated with worsened histopathology and usually impaired survival when compared with SCID mouse controls. When pretransplantation conditioning with irradiation, antiasialo GM antibody and polyethylene glycol-conjugated IL-2 was used, prolonged hu-PBL engraftment was also documented, but this did not affect survival from T. gondii infection when compared with similarly conditioned SCID mouse controls. The latter conditioning protocol resulted in hu-PBL SCID mice producing high titre T. gondii-specific antibody after infection. Conditioned hu-PBL SCID mice had evidence of increased T. gondii-induced inflammatory scores when compared with conditioned SCID mice. These models show promise for the study of the pathogenesis of toxoplasmosis and conditioned hu-PBL SCID mice may have applications for the evaluation of novel therapies for toxoplasmosis in immunocompromised humans.

Effect of route of infection on outcome ofToxoplasma gondiiinfection in hu-PBL SCID mice

“…The ready detection of mRNA for human β-actin (used as a surrogate marker for engrafted human cells) in liver, spleen and lung following oral infection with bradyzoites of T. gondii differed from the lower levels seen in our previously reported analysis of mice infected IP with cysts [6]. This may have been due to the diffi culty in preparing a reliable inoculum using low doses of cysts, so a direct comparison of the infl uence of the two routes on infection with bradyzoites was performed.…”

“…Flow cytometry was also used to examine spleen cells from orally-infected animals and the percentage of human T cells were no higher (not shown) than those found previously in IP infected animals [6]. Engraftment of B lymphocytes was confi rmed through the presence of human IgG in serum.…”

“…oral) resulted in a different outcome of infection when compared to IP infection using an avirulent human isolate of T. gondii [6]. This required an initial dose-ranging study to optimize the inoculation size.…”

“…SCID mice (5 per group) were conditioned by irradiation and anti-asialo GM 1 antibody treatment as previously described [6] and infected orally with 10 3 , 10 4 or 10 5 bradyzoites. The mice were examined daily and the morbidity results are shown in Fig.…”

“…We have previously described a murine model based on the use of immunodefi cient SCID mice into which human PBL are engrafted (hu-PBL SCID) 1 week prior to IP infection with the relatively avirulent DAG strain (which was originally isolated from an immunocompromised human) of T. gondii [6]. The grafts contain a mixture of monocytes, B and T lymphocytes which have the potential for interacting when challenged by specifi c antigens.…”